Apple employing improved compression for new iTunes 1080p videos

An analysis of 1080p TV shows recently added to iTunes has revealed that Apple is using more advanced compression techniques to keep file sizes from becoming unwieldy.

Apple announced on Wednesday that it was adding high-definition 1080p television content to the iTunes Store. The upgraded videos will be supported by the new Apple TV and the third-generation iPad, which packs more pixels than a 1080p television.

After comparing relative file sizes and video quality of the 720p and 1080p versions of iTunes content, ArsTechnica reported on Thursday that 1080p versions (1,920 x 1,080 pixels) were on average just 1.5 times larger than their 720p counterparts (1,280 x 720 pixels), despite having 2.25 times the number of pixels.

The report noted that the limited increase in file size is likely due to Apple's support support for the High profile for compression of H.264 videos. New High profile decompression algorithms on Apple's devices, including the Apple TV, iPad and iPhone, represent an improvement over the Main or Baseline profiles utilized in older devices.

Based on the tech specs for recent devices, Apple appears to have introduced the High profile for H.264 video via its A5 chip. The third-generation iPad, iPhone 4S, and the iPad 2 all support a decoder level of 4.1, which sets a maximum bitrate of 62.5Mbps for the High profile, while the new Apple TV, which sports a single-core A5 processor, has a maximum level of 4.0 (25Mbps). By comparison, the A4-equipped iPhone 4 and Apple TV support H.264 video with a Main profile at level 3.1 (14Mbps).

Report author Iljitsch van Beijnum went on to note that, in some cases, the 1080p version of iTunes TV shows was "pretty much indistinguishable" from the 720p version, though some shows and scenes did show noticeable improvement with the higher resolution. For instance, van Beijnum found that an episode of The Big Bang Theory didn't always show improvements with the 1080p version, though a side-by-side comparison of one particular frame did reveal improved clarity and detail. The 1080p file size for the episode was 856MB, compared to 743MB for the 720p version.

An episode of Awake, however, was described as always showing "some extra sharpness" in the 1080p version and "significantly better" quality in brighter scenes. As such, the author recommended the 1.75GB 1080p version over the 1.45GB 720p one. The below screenshots were taken from the top left corner of both versions of the file while playing back at 1080p (meaning the 720p version was zoomed as it would be on a 1080p flat panel).

It would be interesting to see a grab from the BluRay of this ep as a comparison benchmark. Anyone got it and can throw it up?

The thing to keep in mind with all these lower bit-rate codecs is that they always look better in motion than in screen grabs.

That's an interesting request. It really doesn't have to be from these clips. Any three clips would do. Plus, if one could add in other streaming video, say Netflix's 1080p to see the quality difference when blown up.

The quality of the video depends on how it is shot. I know the video engineer on "Big Bang". He is using Sony F900 cameras to shoot the series. It's shot in 1080i. So watching it at 1080p will mean nothing. It won't look any better at 1080p since it wasn't shot with that increased definition.

They will use newer cameras next season so you may notice an improvement.

So if the new Apple TV can only do High Profile 4.0, does that mean that even if it is hacked to run, say, XBMC, it will never be able to play my Blu-ray rips because 4.0 only can do 25Mbps, whereas Blu-rays can go up to 40Mbps?

Right now, the 1080p iTunes vids I've checked out have a data rate of 5159 kbits/s, or 5.16 Mbps. That means there's still LOADS of headroom under the 25 Mbps ceiling if they want to increase the data rate.

how does one know if the video is 1080p or 720p? does iTunes give it a new icon?

The icon is just "HD" regardless of the resolution. Of note is the left side of the icon is clipped off. This wasn't the case in any previous version of iTunes.

And iTunes now automatically assigns this icon to media if it's 720p or above. Previously if you added your own HD content, you had to use Subler to manually add the HD icon.

And I hate that. Because I have a few 720p things, and that's not HD to me. I don't want to see them as such. My intent is to move my entire catalogue to 1080p, and I can't do that as easily when I have to check every time whether it's a 1080 file or not.

Quote:

Originally Posted by 11thIndian

For 720, I see an "HD•SD" icon, while the 1080 files are "HD" only.

Wouldn't that be because the file has both HD and SD versions in it? Not anything to do with the resolution itself?

I set the desired resolution in iTunes prefs to 1080p ... the latest episode of Happy Endings downloaded at 1080p ... iTunes just has the HD icon (it hasn't downloaded SD versions in a while like it used to with the HD ones) ...

the actual file is named 17 The Kerkovich Way (1080p HD).m4v as opposed to the last episode: 16 Cocktail & Dreams (HD).m4v but I haven't seen anywhere in iTunes that surfaces the difference (other than the Video Dimensions section of the Get Info Summary tab of the file)

I used to see that for 720p stuff ... but the SD versions stopped downloading a while ago ... now I just get the HD version from TV Show subscriptions (if I manually select an episode to buy it still gives me both versions though)

I was hoping for a HD720p and HD1080p icon (or something) to differentiate the different resolutions